Myth Busting: Truth about High Octane

Automotive Industry, like any other, has been maligned with ‘myths’ which are presented and repeated many times that people ultimately start to believe it. Unsurprisingly, many of these myths are related to getting better consumption, increasing the power of the vehicle or some covert aspect of internal combustion engine. Gasoline can be a confusing topic, and it is easy to make assumptions about it that may seem logical, which on closer examination, turn out not to be true. A perfect example of this practice can be seen with octane ratings.

What are octane ratings? In Pakistan, we normally encounter two types of petrol quality on the fuel stations. ‘Regular Plus’, ‘Super’ are some commercial names for Research Octane Number (RON) 87 quality petrol sold in the country and High Octane Blended Component (HOBC) fuel grade which refers to RON 97. I’ll get to the significance of these numbers in a bit.

We tend to associate higher number with better quality. More horsepower, higher torque and more miles out of the fuel are always fancied. This is where the myth of gasoline rating creeps into the picture. Time and again, ‘High octane’ is prescribed to provide better fuel mileage and power as it ‘burns completely’ and locks more energy inside it. These blanket statements are simply not true. In fact, the octane rating for gasoline has nothing to do with the amount of power locked inside of it – it actually relates to just how much a fuel can be compressed before igniting. The higher the number, the less likely it is to ignite under pressure.

Why would you want to put something in the engine that is difficult to burn? To understand the concept of octane rating in the ignition process let us start with a familiar term ‘knock’ or ‘knocking’. When Fuel is sprayed inside the chamber and mixed with oxygen, designers expect it to remain in vapor form until the spark plug lights it up. The timing of this explosion is critical, as gasoline that ignites too early causes ‘knocking’, which reduces engine output and efficiency.

In standard motor, ‘knock’ is rarely an issue because the compression ratio – the pressure that air-fuel mixture is put under in the cylinder – is low enough that the regular octane fuel is sufficient. There is no benefit of running premium fuel in a standard motor, since it will never be able to take advantage of that gasoline’s higher knock resistance. However, more aggressive engine management schemes, especially those found in turbocharged or supercharged vehicles, can turn up the compression to a high level, requiring much higher octane gasoline to avoid knocking.

Fast Facts:

You’ll not get extra power or mileage by running premium fuel in the vehicle, unless the owner’s manual states otherwise. If you are getting better mileage or power, convince yourself that it is all in your head and simply a placebo effect.

On the flip side, running low octane fuel in an engine built for premium fuel can increase the risk of engine damage and will certainly impact that unit’s overall performance.

It is obligatory for all companies oil refineries to produce at least RON 87 petrol by Ministry of Petroleum. All refineries comply with this threshold while Total Oil Pakistan Ltd. sells RON 90 under ‘regular’ grade tag which is a tad higher than the minimum threshold.

All locally manufactured cars require RON 87 petrol which consequently means that all locally produced vehicles come under the umbrella of standard motor.

High octane grade may be used in small quantity if the vehicle suffers from knocking.

So peeps, next time you see a comment ‘only driven on high octane’, do rectify and spread the knowledge. This is what we all are here for.

Aspiring yet chaotic soul, high expectations,child like dreams, engineer by profession, disordered yet floating in the ocean of ideas to make this world a better place and still in the pursuit of finding my 'own self'.
Besides professional commitments, I am a enthused automotive fan. Pakwheels blog is the outlet for all the automotive musings.

“High octane grade may be used in small quantity if the vehicle suffers from knocking.”
1st you said keh octane sai farak nai parta n in the end u said keh engine knock ho to hi-octane dalain.
Kehna kia chah rahay ho bhai?

Uzair Hamid

Although the article is informative, it needs to be rewritten in a much simpler language. A layman like me is still unable to understand what I should be really doing with my Mehran, Cultus, and Civic when it comes to Hi-Octane.

umair

Engine knocking is not an abnormal engine behaviour. High octane is not useful under normal conditions.

and what about total’s RON 90? if that comes under same price range 🙂 I have d17A in my civic with compression ratio of 10.5:1 what would you suggest for that. RON90 or RON87? i know you would not suggest RON97 :p I did not experience any knocking btw…

Abdul Moiz

So what about the Japanese cars such as passo, vitz, mira, axio, premio , prius
Which fuel should be used ?

umair

Minimum RON rating for most of the vehicles is RON87 and that includes JDMs as well

Sulaiman Lalani

i have heard hi-octane gives not better mileage but more than petrol average

Usman Ahmed

automatic transmission cars (specially imported ones) specify that they need high octane fuel to run in their manuals.

Arslan Qamar

are you sure you get what you pay for in pakistan ? RON90 ?

OJ

Great Article, just another clarification that I need . I have 2004 Corolla 1.6 Litre, to improve fuel economy I recently started using full gas tanks of Hi Octane after 3-4 months, the engine developed a strange grinding noise. I had it checked from a number of mechanics even Toyota dealerships however the problem could not be diagnosed. I went through a few blogs and according to them the problem originated from persistent use of Hi Octane, I have reverted to Regular fuel the noise is still there but as you rightly said the fuel economy is almost the same. My question is can Hi Octane be responsible for this damage? As our engines are not designed to run on Hi Octane

Dani Lurka

hmmmmmmm

Drive

Thanks Umair. It was quite informative but a layman like me please tell does it help to use High octane in imported cars ? E.g Will it help my Honda Life if i use HO considerably or even slightly ?

Samad Khan

You forgot one important issue in your article. Engine tuning. Remember that a lot of Jap imports in Pakistan are usually tuned for a higher octane rating from the factory and that is why their engines have terrible knock on local petrol. Since these ECUs are not programmable, there is no way of altering their tuning maps to compensate for the lower octane fuel. Therefore one option is to use hi-octane. This issue was encountered when the previous model (the one before the current) of Honda City was introduced. It had terrible knock issues. Honda had to recall and re-map the ECUs to compensate for the lower octane fuel.

Samad Khan

Its true what Umair says. Knock is abnormal engine behavior and can be triggered by a number of variables. Low octane fuel is one of them. Ever heard a diesel engine? The rattling noise is actually knock. Diesel engines knock by design and that is why they are built with more robust components (hence heavier). High octane will not be of any value to a economy car. You will simply be burning away your money.

Well nice article, i’v red some other articles too, they also says the same that HO prevents engine from knocking. But one thing i observe that HO gives smoother driving experience, even after using a tank of HO if u fill regular fuel in next turn then also u’ll feel smoother drive. an article discribes this is because HO has some engine cleaning compounds. So they recommend, after consuming 3 or 4 tanks of regular gasoline use a tank of HO, this will keep engine clean and running smooth. What u say about this?